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William J. Hodgetts 
towards its growth. In the spring-like winter of 1920-1921 it will 
be noticed that the species reached its maximum very early (January 
1921). ■ 
Aphanochcete prefers low or moderately low concentrations 
between 10 and 17 degrees; high or very high concentrations (as in 
second half of 1919) are particularly harmful. Of course the presence 
of a suitable “host” upon which to grow is essential for this species, 
but in Hawkesley Hall pond fortunately the wide species of CEdogo- 
■nium was.generally so abundant (except in the colder months) that 
lack of a suitable “host” was rarely a factor limiting the growth of 
this epiphyte 1 . But such a condition obtained in April 1920, in which 
year the wide (Edogonium commenced development much later than 
usual (see curve of this species in Fig. 8), and when it did commence 
rapid growth at the end of April and early May the Aphanochcete 
developed pari passu with it until the end of May, when the higher 
temperature stepped in and caused the epiphyte to decline. 
Draparnaldia glomerata attained only one maximum in the pond 
during the period of observation, namely in January 1920 (it was 
“rather common”), when the mean temperature of the air was 
about 5 0 C., and the concentration of the water rather high (falling, 
and between 24 and 20 degrees). The species is undoubtedly a cold- 
water type, and tends to have its maximum development during the 
winter months, as noted by Delf (12), and also by the present author 
in the case of certain other ponds near Birmingham. Why it did 
not appear during the winter 1918-1919 cannot be decided from the 
data available; perhaps the prevailing low concentration of the water 
at that season had something to do with it, or perhaps the species 
was suppressed by severe competition. Its absence in the winter 
1920-1921 was perhaps due to the very mild conditions which 
obtained during that season. During February 1920, towards the 
close of its period of development in the pond, the species produced 
abundant aplanospores. 
XV. NITELLA AND COLEOCH 7 ETE NITELLARUM 
Nitella flcxilis was observed in Hawkesley Hall pond from 1919 
to 1921, and it was always accompanied by Coleochcete Nitellarum, 
an endophytic species which grows between the lamellae of the outer 
cell-walls of Nitella (and Chara spp.). The periodicities of these, two 
species are given in the table below. 
1 Compare in this respect the relation between Nitella and Coleochcete 
Nitellarum in the pond, discussed in the next section. 
